Panels of this type usually have at least one projection towards the vehicle passenger compartment, consisting of the armrest, which is the item closest to the abdomen of the driver, and there is normally a distance of between 7 and 10 mm between the armrest and the thorax. In most cases, these items are produced as panel inserts connected to the panel, although the possibility is not ruled out that the panel is a single part equipped with the said projections.
The context of the invention refers to the contribution of protective measures for the occupants of the vehicle in the case of lateral impact and more specifically to protection for the abdominal area of the occupant.
Throughout this description we shall refer, by way of example, to a panel provided with a panel insert, while understanding that this does not exclude the possibility that the panel might be one single part not equipped with the said panel insert.
As is well known, once the occupant is located in the vehicle passenger compartment, at one side is the door panel with its panel insert, on which different items are housed. The armrest is usually situated at the height of the abdomen and is integrated into the panel insert in the panel. Due to its purpose and the items integrated into it, the armrest protrudes approximately some 60 mm in relation to the panel itself, finishing at a distance of between 7 and 10 mm from the thorax of the user, as indicated above.
In case of lateral impact, once that the door has collapsed and the deformation and force of the impact reach the inner panel, this panel moves towards the occupant and the occupant also moves towards it, and it is the area of the armrest that first reaches the said occupant precisely at the height of the abdomen.
The geometry of the panel insert, with a series of concavities and convexities, has a high level of rigidity in relation to the rest of the panel, so that once it comes into contact with the occupant, it does not absorb the impact as it does not absorb the desired energy levels and transmits levels of force which are higher than acceptable to the occupant.
For the above reasons, the problem which has to be solved is that of penetration of the armrest into the thorax-abdomen area of the occupant in case of lateral impact, so that the levels of force and intrusion that reach the occupant do not exceed certain threshold limits.
As far as is known, there are already several solutions directed towards protecting the occupant in case of lateral impact.
The aim of some of these solutions is to increase the capacity of the door unit to absorb the energy of the impact, so as to reduce the relative acceleration between the occupant and the side panel and so reduce the force of the impact on the thorax.
In one solution, within this trend, at least one additional part is included in the door panel, between the non-visible side of the panel and the inner sheet metal of the door, with these additional parts consisting of a set of walls, ribs or cells that deform plastically to compression and bending during impact, thus absorbing energy.
In the design of these additional parts or items it must be taken into account that the energy has to be absorbed at levels of force and with deformations that do not exceed the permitted thresholds.
This way of proceeding is subject to limitations, especially from the point of view of the need to manufacture additional parts and carry out subassemblies. All this not only increases the cost and the weight of the resulting unit, but also the removal time, if this were possible, reducing their recyclability.
Besides this, the height of the ribs and the areas where they can be situated is limited by the space available between the door panel and the metal structure of the said door.
Another of the known solutions consists of the use of materials with a capacity to absorb energy by means of plastic deformation at some levels of force and deformation that make them ideal for this application.
Among these materials are polyurethane foams and expanded polypropylene in different densities. The material, in blocks, is also placed between the inner panel and the inner sheet metal of the door, forming a sandwich structure, and its effectiveness will depend on the density of the open cells made in the added material.
The limitations of this way of proceeding coincide with those of the previous case.
Another known solution avoids the manufacture and assembly operations mentioned above by manufacturing the door inner panel with the energy dissipation item already incorporated and forming one single part. In this case, the non-visible side of the panel is provided with a series of latticed ribs, which can be either connected with each other or not, giving rise to a cell configuration, which is deformed plastically in case of impact.
Although this solution does not have the disadvantages of having additional parts, subassemblies, cost increases and recycling difficulties, it is however limited by the space that exists between the door panel and the metal structure of the door, and by the increase in weight of the resulting part.
In the particular case of the pillars of the vehicle passenger compartment, other materials are also used, such as impact modified Acrylonitile butadiene styrene (ABS) and mixtures of polycarbonate/PBT, whose performance to temperature variations is more stable.
The main purpose for the use of these materials is that in case of impact, the parts do not suffer brittle fracture and therefore no sharp edges are created that might cause lacerations to the occupant of the vehicle.
Nevertheless, they have the disadvantage that the materials developed for this purpose have a higher cost than those more generally used.
Other types of solutions protect the occupant of the vehicle by dampening the impact against the door panel, for instance by using side airbags or inflatable tubular airbags
Obviously, the main disadvantage of these systems lies in their complexity, as for them to come into action, they must be fitted with acceleration sensors whose response time, must be very short. Moreover, the side panel and the whole door in general has to be prepared in order to house the system, with the consequent space limitations and the design complexity that this involves, all of which results in a higher cost than those of the previous solutions.